This invention relates to slit lamp microscopes. Slit lamp microscopes are principally used for the examination of the anterior eye regions of subjects. They usually consist of a slit illumination means that projects a slit-shaped spot of light into the eye of the subject and a stereo microscope with which the examining doctor observes the slit image. The microscope and the slit illumination means are mounted on a special slit lamp device base with which the slit lamp and the microscope can be simultaneously aligned with the eye of the subject. The chin rest for the subject is also arranged on the device base. Such slit lamp microscopes are described, for example, in the brochure "Ocular Examination with the Slit Lamp" with the printer's imprint K30-115-E-MAII/81 NOO.
Slit lamp microscopes have been used for a long time in ophthalmology, so that ophthalmologists already possess much experience in diagnosing eye diseases by means of the slit images observed with the stereo microscope. However, it is disadvantageous that the observed images are composed of light reflections and scattered light from different depth regions of the eye. The observation of individual, special planes is not possible with such slit lamp microscopes.
The return reflections from the cornea of the subject's eye using equipment in which the slit illumination is projected coaxially with the observation beam path has been found to be particularly trouble some. The relatively strong corneal reflection is then superimposed on the image of the interior of the eye. It is therefore proposed in German Offenlegungsschrift 3,714,041 to arrange a slit diaphragm that corresponds to the slit diaphragm on the illumination side in an intermediate image plane in the neighborhood of the ocular of the microscope. The corneal reflection is to be filtered out by the slit diaphragm arranged in the region of the ocular. By synchronous motion of the slit diaphragm on the illumination side and the slit diaphragm on the observation side, different regions of the subject's eye can be illuminated and observed. The observation of sectional planes of the subject's eye perpendicular to the axis of the eye is, however, not possible with this apparatus, because the slit diaphragms have a depth selective action only perpendicularly of the slit direction. Moreover, the conventional slit lamp illumination in which the slit is projected obliquely of the axis or of the axes of the microscope is not possible with this special equipment.
For examination of the background of the eye, an ophthalmoscope is known, for example, from U.S. Pat. No. 4,900,145, which consists of a conventional slit lamp and a microscope, and in which, in addition, a laser beam is reflected into the beam path of the slit lamp and is focused in the patient's eye. The back-scattered laser light is reflected onto a detector within the microscope. A slit diaphragm is furthermore arranged before the detector, in order to suppress undesired scattered light. The conventional slit illumination is used solely to determine the position of the laser focus within the eye. Thus slit illumination and laser beam illumination are conducted in a common beam path. Even this apparatus does not make possible the visual observation of given sectional planes within the subject's eye.
In conventional microscopy, so-called Nipkow microscopes are known, for example from U.S. Pat. No. 3,926,500; U.S. Pat. No. 4,884,880; and U.S. Pat. No. 4,927,254; and the article "Confocal Scanning Optical Microscopy" in Physics Today, September 1989, pp. 55-62. In such Nipkow microscopes, a Nipkow disk is rotatingly arranged in an intermediate image plane between the objective and the oculars. The Nipkow disk itself is opaque and has a large number of transparent holes arranged along several Archimedean spirals. Each of these transparent holes then acts simultaneously as a confocal illumination and observation diaphragm. Thus the result is that essentially only the light scattered or reflected into a plane conjugate to the plane of the Nipkow disk is transmitted through the holes of the Nipkow disk and hence reaches the ocular. A point-wise assembled image of a special sectional plane thus arises in the ocular. The individual transparent holes are moved through the image field by rotation of the Nipkow disk, so that with a sufficiently dense arrangement of the spirals and with a sufficiently high rate of revolution of the Nipkow disk a stationary, flicker-free image of a depth section is generated.
The use of such Nipkow microscopes in opthalmoscopy is still quite unknown. Hence it is very difficult for the ophthalmologist to diagnose eye diseases on the basis of depth sections through the eye observed with a Nipkow microscope.